Fixes README example

lib/README.md

@@ -37,7 +37,7 @@ let store = Store::new().unwrap();
 // insertion
 let ex = NamedNode::new("http://example.com").unwrap();
 let quad = Quad::new(ex.clone(), ex.clone(), ex.clone(), GraphName::DefaultGraph);
-store.insert(&quad)?;
+store.insert(&quad).unwrap();
 
 // quad filter
 let results = store.quads_for_pattern(Some(ex.as_ref().into()), None, None, None).collect::<Result<Vec<Quad>,_>>().unwrap();